Seventy-six years ago, Franklin Delano Roosevelt took to the inaugural dais and reminded a nation that its recent troubles “concern, thank God, only material things.” In the midst of the Depression, he urged Americans to remember that “happiness lies not in the mere possession of money” and to recognize “the falsity of material wealth as the standard of success.”

“The only thing we have to fear,” he claimed, “is fear itself.”

As it turned out, Americans had a great deal more to fear than that, and their innocent belief that money buys happiness was entirely correct. Psychologists and economists now know that although the very rich are no happier than the merely rich, for the other 99 percent of us, happiness is greatly enhanced by a few quaint assets, like shelter, sustenance and security. Those who think the material is immaterial have probably never stood in a breadline.

Money matters and today most of us have less of it, so no one will be surprised by new survey results from the Gallup-Healthways Well-Being Index showing that Americans are smiling less and worrying more than they were a year ago, that happiness is down and sadness is up, that we are getting less sleep and smoking more cigarettes, that depression is on the rise.

But light wallets are not the cause of our heavy hearts. After all, most of us still have more inflation-adjusted dollars than our grandparents had, and they didn’t live in an unremitting funk. Middle-class Americans still enjoy more luxury than upper-class Americans enjoyed a century earlier, and the fin de siècle was not an especially gloomy time. Clearly, people can be perfectly happy with less than we had last year and less than we have now.

So if a dearth of dollars isn’t making us miserable, then what is? No one knows. I don’t mean that no one knows the answer to this question. I mean that the answer to this question is that no one knows — and not knowing is making us sick.

Consider an experiment by researchers at Maastricht University in the Netherlands who gave subjects a series of 20 electric shocks. Some subjects knew they would receive an intense shock on every trial. Others knew they would receive 17 mild shocks and 3 intense shocks, but they didn’t know on which of the 20 trials the intense shocks would come. The results showed that subjects who thought there was a small chance of receiving an intense shock were more afraid — they sweated more profusely, their hearts beat faster — than subjects who knew for sure that they’d receive an intense shock.

That’s because people feel worse when something bad might occur than when something bad will occur. Most of us aren’t losing sleep and sucking down Marlboros because the Dow is going to fall another thousand points, but because we don’t know whether it will fall or not — and human beings find uncertainty more painful than the things they’re uncertain about.